Biomes Major ecosystems found in large geographic regions characterized by a distinct vegetative community --primarily a result of abiotic processes Physiognomy The overall appearance of a biome or community based on the relative density, height, and shape of its dominant vegetation

Six major biomes: 1. tropics 2. grasslands/savannah 3. temperate forests 4. coniferous forests or taiga 5. tundra 6. deserts

Fig Minor biomes: 1. chaparral 2. temperate rain forest 3. polar regions

Fig. 24.4

Tropical Biomes : Most occur within 10° latitude Defined by rainfall > 240 cm per year Temperature and moisture not limiting factors, nutrients and light are

Amazon (Neotropics) Congo SE Asia New World Old World

Misconceptions about tropics: Soils are rich Climate is stable Jungles are dense

dense canopy, stratified up to four levels Physiognomy of Tropics high diversity of trees trees per hectare species represented low population densities for each

Humidity ~70% Humidity 90-95% Temperature gradient Fig High light attenuation

Leaf litter accumulates rapidly, but decays rapidly Plants in competition for nutrients released in decay

Physiognomy of Tropics shallow, spreading roots and leaves with drip tips

Physiognomy of Tropics shallow, spreading roots and leaves with drip tips Mycorrhiza fungi and hyphae buttress and prop roots

Physiognomy of Tropics shallow, spreading roots Mycorrhiza fungi and hyphae buttress and prop roots epiphytes, lianas

Gaps and patch dynamics

Semi-aquatic herbivores Nocturnal frugivores Diurnal herbivores Nocturnal herbivores Ant eaters Parallel Evolution

Hammocks in south Florida

Temperate rain forest: Olympic National Park, WA

Longleaf Pine community of the Southeast

Deserts are defined by rainfall: true desert has < 12 cm/yr extreme desert < 7 cm/yr semi-desert has up to 40 cm/yr evaporation exceeds rainfall

Deserts also characterized by: hot days, cool nights from high albedo sparse plant life C 4 and CAM photosynthesis xerophytes more living plant biomass below ground than above, sometimes 1:10 difference

Four major North American Deserts 1.Sonoran 2.Mohave 3.Chihuahuan 4.Great Basin

Sonoran Desert Lowest, hottest desert up to 120° F in summer Bi-annual rainfall ~18 cm/yr Most diverse desert in NA Saguaro Cactus limited by temperature

Sonoran Desert, AZ cholla cactus ocotilla palo verde trees

Mohave Desert Most precipitation in winter 5-12 cm/yr Higher elevation than Sonoran Plants adapted to cooler temperatures

Joshua Trees

Cholla cactus and yucca

Chihuahuan desert and creosote Most precipitation in summer cm/yr Dominated by low shrubs and cactus

Prickly Pear Cactus

Great Basin Desert Largest U.S. desert, considered a cold desert Elevations range from feet Caused by a series of rainshadow effects Precipitation cm/yr Dominated by sagebrush

Sagebrush dominates

All deserts are characterized by slow growth by plants, but also slow decay of litter Very fragile ecosystems because of this Disturbances, even a single car track, may last decades to centuries Archaeological roads, clearings still visible after years

Kangaroo Rat: Endemic to North America

Kangaroo Rat Adaptations No sweat glands and never drink water Kidneys concentrate urine 5X more than humans Nocturnal behavior, with large auditory bulla Stay in burrows during day, plug entrance and cache seeds Use torpor for brief periods, have bare feet to radiate heat, or cover with tail to retain heat Rostrum long, with complex nasal bones, convoluted surfaces cooled by evaporation to capture water in air leaving body

Jerboa

Sonoran desert exclosure experiment show keystone effect Ants in Deserts high diversity, granivores Chihuahuan desert: 23 spp. in 30 m 2 50 spp. in 3 km transect Australia: 150 spp. in < 1 ha desert grasses dominate